Generally, liquid crystal display devices have been utilized in various fields, for example, in office automation equipments or measuring instruments as display devices small in size, reduced in weight and of low electric power consumption. Among these liquid crystal display devices, while those liquid crystal display devices for displaying graphs or letters have a great number of picture elements, those with relatively small number of picture elements have been made into products or studied in recent years for utilizing liquid crystals as the device for controlling the amount of transmission light such as sun visors for use in automobiles, protection spectacles for welding, protection spectacles for laser beam, helmet shields for use in autobicycles, goggles for use in skiing or autobicycles or liquid crystal shutters for use in three-dimensional television sets. Furthermore, those devices having laminated liquid crystal panels have been made into products or studied, for example, liquid crystal protection spectacles for welding, liquid crystal protection spectacles for laser beams and liquid crystal shutters for use in three-dimensional television sets particularly requiring relatively low transmittance and high contrast.
In a conventional multi-layered liquid crystal display device of this type, one end (upper end) of a substrate is extended than the other to form an electrode lead-out portion and a transparent electrodes are formed to the electrode lead-out portion. The transparent electrodes on one side are collectively disposed at the upper end of the substrate for concentrating the electrodes for applying electric fields to the liquid crystal panels and the situation is the same for the other transparent electrodes, in which two-layered liquid crystal display panels prepared by laminating liquid crystal panels are formed. In such two-layered liquid crystal display panel, a connector corresponding to the thickness of the electrode lead-out portions is fitted and electric fields from an external driving circuit are applied to the liquid crystal panels respectively.
However, the conventional multi-layered liquid crystal display panel of this kind, since a polymer film is used as the substrate and electrodes are formed to the substrate to fit the connector, the transparent electrodes on the substrate made of polymer film are poor to the friction as compared with the liquid crystal panel made of glass, there is a problem that the connection reliability is low.
The present inventor has made an earnest study on such a problem and, as a result, has found an effective countermeasure therefor based on a plurality of inventions regarding the liquid crystal display device that the applicant of the present invention has previously proposed.
One of them is a liquid crystal optical device (refer to Japanese Patent Application No. Sho 61-303207), which intends to prevent the intrusion of obstacles in the precutting step to improve the yield by PF-LCD with less number of picture elements (LCD made of polymer film, PF-Liquid Crystal display), and in which electrodes on upper and lower substrates of an identical configuration are extended in one identical direction and an external circuit substrate is inserted between them. According to this system, the electrodes are highly resistive to friction upon insertion of connectors to improve the reliability in the connection when using the electrodes on external circuit substrates, for example, copper electrodes of FPC (plated with solder, gold, nickel, etc.). The other is a liquid crystal display device (Japanese Patent Application No. Sho 62-15779), which intends to prevent the disconnection of the external circuit substrate by flexion, and in which a recess is disposed to electrode lead-out portions to constitute a connection portion with an external circuit substrate.
As another conventional embodiment, there has been a liquid crystal display device with the number of picture element of one, in which an upper transparent electrode and a lower transparent electrode are formed substantially over the entire surface of upper and lower substrates made of a pair of opposed polymer films respectively, and oriented films are formed by orientation treatment. A gap member is scattered between both of the substrates and both of the substrates are bonded by means of an annular seal member. Liquid crystal is sealed within a seal space defined with the seal member, both of the substrates, etc. and this seal range constitutes a display area. The upper substrate and the lower substrate are extended together with the upper and the lower transparent electrodes from the area to constitute upper and lower electrode lead-out portions.
An external circuit substrate is inserted between both of the electrode lead-out portions.
The external circuit substrate is extended and protruded in the direction in perpendicular to the direction of extending both of the electrode lead-out portions and an external driving circuit is electrically connected to the protrusion portion.
By the way, in such a constitution, it is desirable to reduce the thickness of the external circuit substrate.
That is, if the thickness of the external circuit substrate is reduced, the distance between the external circuit substrate and the seal material can be shortened within such a range as not causing the detachment of the seal material, thereby enabling to decrease the size of the device. In this case, the cell gap can not be made so large.
However, in such a constitution, since the thickness of the external circuit substrate is reduced and the external circuit substrate is supported only on one side, the external circuit substrate tends to be flexed at the end of the supported portion thereby possibly causing disconnection. By the way, it may be considered to reinforce the end of the support portion by disposing a coverlay film there. However, since the thickness is increased only in that portion by the disposition of the film and the thickness for the entire external circuit substrate is made uneven, heating and pressing become not uniform to bring about a problem in view of the accuracy for the hot-pressing.
By the way, the liquid crystal display panel is generally constituted with a gap from several microns to several tens microns and, accordingly, the seal member for sealing liquid crystal is formed with the same extent of thickness as that of the gap. Further, if the thickness of the upper and the lower substrates made of the polymer film is set to 0.1 mm, the thickness of the external circuit substrate including the upper external electrode and the lower external electrode, etc. is usually from about 0.1 to 0.2 mm. Accordingly, the thickness of the external circuit substrate is greater than the gap of the seal material and detachment of the seal material from the upper and the lower substrates is prevented by disposing the end of the external circuit substrate with 1 to 2 mm distance from the end of the seal material.
Such a constitution has a merit that the upper and the lower substrates of an identical shape can be used with no undesired effects on the liquid crystal portion, etc. as the constitution of electrode lead-out portions of liquid crystal display panels in which an external circuit substrate that is flexible printed substrate thicker than the gap of the seal material is bonded between two of upper and lower substrates by using heat seal connectors. However, the upper transparent electrode and the lower transparent electrode at the inside of the upper and the lower substrates of a hollow chamber between the seal member and the end of the external circuit substrate may cause short circuit due to the urging force from the outside or due to the deformation of the polymer films caused by the change in the circumstantial temperature and humidity.
For preparing a liquid crystal display device of the conventional example described above, a polymer film attached with a transparent electrode at first cut-into a work size. Then, an electrode pattern is formed, orientation agent is printed and rubbing treatment is applied. Then, cutting referred as pre-cutting is applied to the polymer film to form cutting lines for the upper substrate and cutting lines for the lower substrate. Then, a pair of polymer films formed with such upper and lower cutting lines are appended with each other and then applied with final cutting.
However, in such a conventional liquid crystal display device, since pre-cutting is applied before appending the upper and the lower electrode lead-out portions, film dusts are resulted upon cutting, which may deposit to the orientated films oriented to the upper and the lower transparent electrodes and incorporated as obstacles in the liquid crystals to worsen the performance of the product.
While on the other hand, the device as disclosed in Japanese Utility Model Application No. Sho 61-123537 is adapted such that an electroconductive film from a driving circuit is inserted between transparent electrode substrates, an electroconductive member is disposed between the film and both of the transparent electrode substrates, and the transparent electrode substrates and the driving circuit are electrically connected by way of the film.
However, in such a device, since the gap of the liquid crystal cell, that is, the gap between both of the transparent electrode substrates is several microns, the thickness of the electroconductive film to be inserted in the gap has also to be set to several microns and the actual use of such a thin electroconductive film causes a problem.
The first object of the present invention is to provide a multi-layered liquid crystal display device capable of improving the reliability upon connection with the connector in a simple structure.
The second object of the present invention is to provide a liquid crystal display device capable of preventing the disconnection in the external circuit substrate with no increase in the thickness of the substrate than usual.
The third object of the present invention is to provide means capable of preventing conduction between each of the transparent electrodes on the upper and the lower sides in the space chamber portion between the seal member and the external circuit substrate in a liquid crystal display device, in which upper and lower substrates made of polymer films are extended to constitute connection electrode portions with respect to the external circuit substrate.
The fourth object of the present invention is to provide a liquid crystal display device that can prevent the incorporation of obstacles in the display area, can be manufactured with ease and shows high reliability upon use.